1. Field of the Invention
The present invention relates to a method for pre-treating an epitaxial layer, a method for evaluating an epitaxial layer, and an apparatus for evaluating an epitaxial layer. Specifically, the present invention relates to a method for pre-treating an epitaxial layer a method for evaluating an epitaxial layer, and an apparatus for evaluating an epitaxial layer, which enable stable measurement of resistivity of the epitaxial layer.
2. Description of Related Art
Recent remarkable progress of the integrity of silicon semiconductor devices requires a strictly high quality of silicon wafer as a substrate for the semiconductor device.
For example, since crystalline defects such as dislocations and metallic impurities cause an increase of leak current and reduction of carrier-lifetime, reduction or elimination of the crystalline defects and metallic impurities from a device active region as a region for forming devices on a wafer is strictly demanded compared with the conventional level, in order to satisfy refinements of circuits with increasing integrity.
In order to satisfy such demands, an epitaxial wafer has been developed by growing an epitaxial layer substantially free of crystalline defects on the wafer, and frequently used in the manufacture of highly integrated devices.
A p+ type or n+ type silicon wafer doped with boron or phosphor to a high concentration has been used as a wafer for growing an epitaxial layer thereon. A N type or P type epitaxial wafer is produced by forming a p− type or n− type epitaxial layer doped with boron or phosphor to a low concentration on the p+ type or n+ type silicon wafer.
Characteristics of the epitaxial wafer when checked for quality control include the resistivity of the epitaxial layer, flatness of the epitaxial layer, and warpage of the epitaxial wafer, and haze of a surface of the epitaxial wafer. Especially, correct measurement of the resistivity is required since the resistivity is the most fundamental property of the wafer. Conventionally, the Hg-CV measurement belonging to capacitance-voltage measurement has been widely used as a method to measure the resistivity of an epitaxial layer of the above-described N type or P type epitaxial wafer. In the Hg-CV measurement, an oxide film is firstly formed on the surface of the epitaxial layer, and the oxide film is made to contact with a mercury electrode, thereby forming a so-called Schottky junction. Next, with the Schottky junction intervening, property of the capacitance (C) and electric voltage (V) in the reverse direction are measured. The resistivity of the wafer can be determined based on the measurement result of the C-V property and donor concentration. Japanese Unexamined Patent Application, First Publication No. H6-140478 (Patent reference 1) describes an apparatus for measuring the resistivity of an epitaxial layer based on a principle of the HV-CV measurement.
As a method for forming an oxide film on the surface of an n-type epitaxial layer, there is known a method standardized by ASTM F1392. In this method, a wafer is immersed for several minutes in a solution containing an oxidizing agent such as hydrogen peroxide, subsequently cleaned and dried. By this treatment, a thin oxide film is formed on the surface of the wafer.
However, in this method, a large amount of the solution containing the oxidizing agent are required, and a relatively long treating-time of about 20 to 30 minutes. In addition, there is a possibility that a long treating-time results in a delay of feed-back of measurement results of resistivity in the manufacturing process of epitaxial layers.
On the other hand, in the standard pretreatment-method of a p-type epitaxial layer, a wafer is immersed in a HF solution, subsequently rinsed in pure water, dried by spinning, and is subjected to Hg-CV measurement. Although this method allows measurement of resistivity of the p-type epitaxial layer, there is a demand for further reducing dispersion of the measured value. In an alternative method recently proposed for oxidizing n-type wafers (patent reference 2: Published Japanese Translation No. 2002-516486 of PCT International Publication), ultraviolet (UV) light is irradiated to the wafer placed in an oxygen bearing atmosphere, thereby generating atomic oxygen or ozone and oxidizing the wafer by the atomic oxygen or by the ozone.
On the other hand, in a method proposed for treating a p-type wafer, an inert carrier gas is blown into the acid trap containing hydrofluoric acid, and a surface oxide film of the wafer is removed by the carrier gas.
However, even in the method described in Patent Reference 2, depending on the pretreatment conditions such as irradiation time of UV light, a dispersion in measured resistivity could not be avoided.
Based on the above-described circumstances, with regard to an n-type epitaxial layer, an object of the present invention is to provide a method for pre-treating the epitaxial layer, method for evaluating the epitaxial layer, and an apparatus for evaluating the epitaxial layer, which enable a reduction of consumption of the agent for pretreatment, shortening of treatment time, and reduction of dispersion of the measured value.
In addition, with regard to a p-type epitaxial layer, an object of the present invention is to provide a method for pre-treating the epitaxial layer, method for evaluating the epitaxial layer, and an apparatus for evaluating the epitaxial layer, which require a longer time than the conventional method, but enable a reduction of dispersion of the measured value.